This invention relates generally to turbine engines, and more specifically, to flameholders used therein.
At least some know gas turbine engines used with aircraft include in serial flow communication a fan, compressor, combustor, high pressure turbine, and low pressure or booster turbine. High performance aircraft engines may also include an afterburner or augmenter at the engine's aft end for providing additional thrust when required. During engine operation, air compressed as it flows through the fan and compressor, is mixed with fuel in the combustor. The fuel/air mixture is ignited and the combustion gases are channeled downstream through the turbines which extract energy therefrom. The hot combustion gases are then discharged from the engine into an augmenter wherein a portion of the exhausted gas is mixed with fuel and reignited prior to being discharged from the engine through a variable area exhaust nozzle.
Known augmenters include an exhaust casing and liner which defines a combustion zone. Flameholders and fuel spraybars within the augmenters introduce additional fuel into the exhaust discharge from the turbine engine. Various types of flameholders are known and at least some augmenters include at least one circumferential flameholder. More specifically, such flameholders include V-shaped gutters which define regions of relatively low velocity in the otherwise high velocity core gases. The afterburner flame may be initiated within such low velocity regions.
At least one known augmenter includes an annular flameholder assembly that includes a row of swirl vanes mounted between radially outer and inner casings. Each of the swirl vanes has opposite pressure and suction sidewalls that each extend from a leading edge to a trailing edge. An aft end of each flameholder includes a generally planar aft panel that extends about the circumference of the flameholder to facilitate holding the flame during augmenter operation. An annular opening defined in an upstream side of the augmenter enables exhaust gases to flow into the flameholder. A flow restricting structure downstream from the annular opening meters an amount of air flow entering the flameholder.
However, in at least one known flameholder, the flow restricting structure creates a flow pattern that extends downstream to the fuel sprayers. The fuel and exhaust flow mixture in such flow patterns may migrate upstream and spontaneously combust within the flameholder. Over time, spontaneous combustions within the flameholder may reduce the useable life of the augmenter.